This invention relates to machinery and methods for recycling used carpets. Such recycling is useful for reclaiming and reusing valuable materials (such as nylon and polypropylene), and for reducing the quantity of solid waste that must be disposed of in landfills.
Today, most carpets that must be discarded (either because they have become badly worn after use, or because they do not meet appropriate quality standards after manufacture) are buried in landfills, or burned in incinerators. These are not ideal methods of disposal, and it is preferable to recycle them in some manner which reuses at least some of their materials.
Most carpets made today contain pile fibers made of nylon, which are woven through a primary backing layer, then glued to a secondary backing layer. Polypropylene is used most commonly to make both backing layers. Latex mixed with calcium carbonate is used most commonly as the binder/filler material that glues the nylon piles to the polypropylene backing layers. Polypropylene and latex are relatively cheap and strong, which is why they are used so widely in carpet manufacture; by contrast, nylon is substantially more expensive, and it has a substantially higher value when recycled. Latex also has the advantage of being flexible and yielding at room temperatures, so it will not split, crack, or become brittle when carpet is rolled up and then laid flat, during storage, handling, and laying.
Several types of carpet recycling processes have been developed, which use a variety of different approaches that can generally be grouped into three categories. In one category, a grinding or shredding machine chews up an entire segment of carpet, leaving the nylon mixed together with the polypropylene and latex. The composite mixture that results is used as a relatively low-grade plastic, for purposes such as molded park benches.
A second type of system tries to break apart and loosen the latex binder that holds nylon piles to backing layers; see U.S. Pat. No. 5,230,473, by Hagguist and Hume 1993. This allows the nylon pile fibers to be pulled out of the backing layer, using rollers that contain various types of small claw-type fingers that engage and pull at the nylon pile fibers while the backing layer (which remains intact) continues to travel upon a flat conveyer system. This type of system generates reclaimed nylon that is substantially purer and more valuable; however, it is substantially more expensive to operate, and requires certain types of liquid solvents to loosen and remove the latex. It also requires removal of the liquid solvents from the reclaimed nylon.
A third type of system cuts carpet segments into relatively small chunks, which are then grinded or pulverized into tiny fragments. These fragments are then passed through centrifugal separators, to try to separate most of the polypropylene, latex, and calcium carbonate particles, which are relatively dense, from the nylon pile material, which is less dense.
None of these systems have reached a point where they are entirely satisfactory, as evidenced by the fact that carpet recycling is still in a stage of struggling infancy. There are very few successful and profitable operations anywhere in the U.S., despite the fact that more than 4 billion pounds of carpet are discarded every year in America. Presently, the very large majority of that discarded carpet goes into landfills.
Currently, claw drums that are used in certain types of carpet shredding operations (in the first category of recycling systems, listed above) have a design which can be referred to as an "open culinder". One such device is shown in U.S. Pat. No. 3,780,399 (Morel, 1973, assigned to Laroche Machines, of Cours, France; also illustrated in the Laroche sales brochure for the "Horizontal heavy opener, Picker type"). This drum (and various other types of carding and combing rollers, as described below) is mainly used in "fiber opening" operations, in which balls, clumps, or mats of cotton or other fibers must be opened up and pulled apart, so that the fibers can be turned into threads, for weaving or other use.
The Laroche type of "open drum" comprises a series of claw-tooth mounting bars that are spaced apart from each other, in a cylindrical arrangement. The claws are emplaced in these bars by sliding a series of claw-tooth bases into an accommodating groove in a mounting bar; for example, if the claw-tooth bases are T-shaped, the accommodating grooves will be rectangular. Such systems, with rows of teeth mounted in bars, are illustrated in U.S. Pat. Nos. 3,445,895 (Barbod 1969) and 4,797,977 (Napoleon et al, 1989).
There are at least two major problems with open drums, when used for carpet shredding. First, if a single claw-tooth in a row pf claws gets broken (or unacceptably worn and dull) and must be replaced, it usually is necessary to remove all of the claws on one side of that claw, by sliding all of them out of the bar, before the broken or worn tooth can be accessed and removed. This can be a difficult, cumbersome, and time-consuming operation, particularly in view of the second problem with such systems.
The second problem with open drums in carpet shredding operations is that they are working in an environment that is constantly being surrounded by extremely high levels of airborne particulates and fibers. As a segment of old, dirty carpet is shredded by a rotating claw drum, it rips apart (1) the semi-brittle latex binder (with calcium carbonate) that was used to glue the nylon pile to the polypropylene backing layers; (2) the relatively thick and stiff glue-covered strands of the polypropylene backing layers; and (3) the nylon pile material. All of these components, plus any dust and dirt that was pushed into the carpet during years of use, are being ripped apart at high speed.
To try to minimize the dangers of such particles in the open air (and to minimize noise levels as well), claw drums that are used to shred carpet are always operated inside a surrounding hood or cowl, made of sheet metal. Air is constantly being sucked out of these hoods by a vacuum system, which carries the air-borne particulates to a filter system which collects them, so they can be disposed of as solid waste rather, than discharging them into ambient air which people are breathing.
Despite the use of such vacuuming systems, a very high level of airborne dust, particulates, and fibers constantly surrounds a claw drum whenever it is actively shredding carpet. This mixture of dust, particulates, and fibers works its way into any and all cavities and openings in and around the teeth and the mounting bars of the claw drum. This is undesirable, for various reasons; in general, particulates and fibers can jam up bearings, joints, or other operating mechanisms, and can also cause abrasion which reduces the operating life of the various components. To avoid such problems, a "solid-face" claw-tooth drum would be preferable, in which the claws extend outwardly from a solid and impermeable cylindrical face that does not allow any dust, particulates, or fibers to work their way into the internal mechanisms of the cylinder while it is being used to shred carpet.
Other types of cylinders, with long narrow tines that protrude from a solid cylindrical face, have been developed for combing operations, where the operating requirements and goals are substantially different than for carpet shredding. Such cylinders are described in, for example, British patent 2,035,402 A (Kanai, published in June 1980). FIG. 1 in that patent purports to show a conventional (prior art) combing device, in which various "needles" are inserted into flat "needle plates". A number of such needle plates, with needles inserted, are then stacked together to form a rotating combing device. That British patent criticized the previous methods of constructing such plates, and disclosed a purportedly superior design that used angled "7"-shaped insertion slots for the needles. It should be noted that in both the conventional design and in the newly-patented design shown in the British patent, a single needle, if damaged, could not be removed from its holding plate, due to the presence of a protrusion on the side of the needle. Accordingly, a different removal procedure for dealing with a damaged needle is described in lines 30-43 of page 1.
A somewhat similar arrangement, apparently for a conventional prior art combing device, was illustrated in FIG. 1 of Japanese patent 60-75618. As in the British patent, a damaged needle could not be removed by itself, without somehow opening up or removing the plate and cutting through the "sash" bar that was inserted through an entire row of needles. That patent purported to show an improved design, in which individual needles apparently could be inserted and removed due to a different design; however, in that purportedly improved design, the needles themselves did not protrude out from a solid cylindrical face. Instead, each needle was provided with a pair of flanking "shoulder" surfaces which, if properly lined up together with the shoulders of other such needles, would generate a relatively smooth cylindrical surface at the base of the protruding the needles. A visual examination of the improved design in FIG. 2 of Japanese patent 60-75618 suggests that that design, which was intended as a combing device, would not be nearly strong enough and durable enough for reliable use in shredding carpet, which presents an entirely different set of challenges and obstacles that must be overcome.
As noted above, these combing systems have never been adapted to other machinery for shredding carpet segments.
One object of the subject invention is to disclose an improved heavy-duty claw-tooth drum which can rip apart and shred segments of discarded carpet into a combination of (1) chunks or strands of polypropylene backing material, and (2) strands of nylon pile material, while eliminating any processing steps that might otherwise be required to remove intact segments of polypropylene backing material from the nylon pile material.
Another object of this invention is to disclose an improved processing system for recycling segments of discarded carpet, in which an improved claw-tooth drum interacts with other processing devices, to rip apart segments of discarded carpet, and subsequently to separate particles and strands of polypropylene backing material from nylon pile material, while eliminating any processing steps that would otherwise be required to remove intact segments of polypropylene backing material from the nylon pile material.
Another object of this invention is to disclose an improved claw-tooth drum which has a solid, closed, impermeable cylindrical face, through which any desired number of claws protrude. By providing a solid closed face (rather than an open-faced cylinder comprising spaced bars for mounting the claws), the improved claw drum resists fouling and clogging of the cylinder and various internal mechanisms due to accumulation inside the cylinder of polypropylene and nylon fragments, latex particles, and dust, which are generated in copious quantities whenever carpet segments are ripped apart by claw drums rotating at fairly high speeds.
Another object of this invention is to disclose an improved claw drum in which a worn or broken claw, at any location on the surface of the drum, can be easily replaced, by itself, without having to move or adjust any other claws.
These and other objects of the invention will become more apparent through the following summary, drawings, and description of the preferred embodiments.